WO2002043226A1

WO2002043226A1 - Device comprising a rotary electric machine

Info

Publication number: WO2002043226A1
Application number: PCT/FR2001/003747
Authority: WO
Inventors: André Gennesseaux
Original assignee: Energiestro
Priority date: 2000-11-27
Filing date: 2001-11-27
Publication date: 2002-05-30
Also published as: FR2817404B1; AU2002222060A1; FR2817404A1

Abstract

The invention concerns an electric machine specially designed to work in a vacuum, comprising a rotor (14) provided with four teeth (16) which cover each an angular sector of about sixty degrees and a stator (15) provided with twelve teeth (17) which cover each an angular sector of about thirty degrees, a coil (18) being wound around each tooth (17) of the stator (15). One coil (18a) out of two is energised by a current and the six other coils (18b 18d) are assembled in pairs to form three phases. The teeth (16, 17) are arranged such that the total reluctance of the magnetic circuit enclosing the coils is constant during the rotation of the rotor.

Description

DEVICE COMPRISING A ROTATING ELECTRIC MACHINE.

The present invention relates to devices comprising rotating electrical machines, in particular those specially designed to work in a vacuum, and more particularly those designed to be mounted on energy storage flywheels.

Energy storage by flywheel is a well-known technology, even if it is not used in common. However, it has many advantages when compared to the most used storage technology: the electrochemical battery. In particular, a flywheel can be worn out, while the life of a battery is extremely short in terms of number of cycles: a few thousand at most. The efficiency of a steering wheel can be excellent, while that of a battery is around 50%. It would therefore be very advantageous to be able to have energy storage flywheels to replace the batteries. However, it turns out that the electrical machines (engine and / or generator) which have been proposed so far for connecting the steering wheel to the outside are not satisfactory.

The most important constraint comes from the fact that a flywheel must turn in a rarefied atmosphere in order not to dissipate its energy in friction, while most electric machines are designed to turn in the air. This prohibits the use of rotating collector machines, as it is known that the service life of a collector in a vacuum is very short. It also prohibits machines with rotor conductors, as it would be impossible to dissipate the heat produced by the Joule effect.

Some have proposed permanent magnet machines to the rotor, but these machines have two major drawbacks: their no-load losses are very high, and the voltage they produce varies with the speed of rotation.

Recently the American company Active Power has put on the market a machine with zero sequence technology, described for example in American patent US-5,969,457. In this technology, a coaxial coil with the flywheel is traversed by a direct current which creates a field permanent magnetic excitation through the flywheel (which must be magnetically permeable) and the stator. Teeth are cut in the flywheel to concentrate the magnetic field. It suffices to place induced coils opposite the teeth to obtain an alternating voltage. This machine solves the previous problems, but it still has drawbacks: the flywheel cannot be optimized for energy storage since it has an electrical role; the flywheel being massive, the variations of the magnetic field in the teeth create eddy currents which dissipate energy and heat the flywheel.

Furthermore, document EP-A-0 348 984 describes a device comprising a rotary electric machine which comprises a rotor rotating around an axis of rotation and a stator, the rotor comprising a plurality of teeth made of divided ferromagnetic material but not comprising neither conductor nor permanent magnet, the stator comprising a plurality of teeth of divided ferromagnetic material, oriented towards the rotor, each tooth of the stator being surrounded by a coil, the coils comprising on the one hand excitation coils which are electrically connected to a control and power unit for receiving an excitation current, and on the other hand, receiving coils adapted to produce an induced voltage when the rotor turns.

This device has the particular disadvantage that the total reluctance of the magnetic circuit varies considerably when the rotor turns. We can indeed note that for certain angular positions of the rotor, there is no longer any magnetic connection between the teeth, which has the consequence that the magnetic excitation flux is zero. The variation of the flux in the magnetic excitation circuit when the rotor turns induces voltage peaks in the excitation windings, very troublesome for the circuit responsible for producing the excitation current.

The object of the present invention is in particular to overcome this drawback.

To this end, a device of the type in question is characterized in that the teeth of the rotor and of the stator are arranged so that the total reluctance of a magnetic circuit formed by all of the teeth of the rotor and of the stator remains substantially constant when the rotor turns.

It will be noted that the word "tooth" used here must be understood as designating a portion of rotor or stator with high magnetic permeability separated from the other teeth by zones of lower magnetic permeability (air, vacuum, solid material of relatively low magnetic permeability , etc.). The teeth according to the invention are therefore not necessarily protruding parts of the rotor or the stator. In preferred embodiments, recourse may also be had to one and / or the other of the following arrangements, where appropriate independently of the arrangements described above: the teeth of the rotor are four in number and each cover a angular sector of about sixty degrees centered on the axis of rotation, said rotor teeth being angularly distributed around the axis of rotation, the stator teeth are twelve in number and each cover an angular sector of about thirty degrees centered on the axis of rotation, the coils of excitation are six in number and are coupled in pairs of diametrically opposite excitation coils, and the receiving coils are six in number and are coupled in pairs of diametrically opposite receiving coils; the teeth of the rotor are three in number and each cover an angular sector of about 'sixty degrees centered on the axis of rotation, said teeth of the rotor being equally distributed around the axis of rotation, the teeth of the stator are one in number of four and each cover an angular sector of approximately ninety degrees centered on the axis of rotation, the excitation coils are two in number and are coupled into a pair of diametrically opposite excitation coils, and the two receiving coils are coupled to a pair of diametrically opposite receiving coils; the rotor teeth are fixed on a flywheel; - the flywheel, the rotor and the stator are contained in a vacuum enclosure; the teeth of the rotor are arranged opposite a radiator integral with the vacuum enclosure, said teeth of the rotor being adapted to dissipate thermal energy by radiation towards said radiator; the teeth of the rotor are independent of each other; the rotor teeth are thermally insulated from the flywheel; - the flywheel is made of austenitic stainless steel; the flywheel has at least one flange which has a radially inner face against which the teeth of the rotor bear; - the rim has a free end extended radially inwards by a tab at each tooth of the rotor, said tab of the rim partially covering the corresponding tooth of the rotor; the rotor tooth is enclosed by a cage which is itself force-fitted between the flange of the flange and a bearing surface belonging to the flywheel, said cage being in abutment against the radially inner face of the flange, and said insulating cage the corresponding tooth from any direct contact with the flywheel; - the cage includes:

. a rear face interposed between the corresponding tooth of the rotor and the radially inner face (23a) of the flange, and several elastic tabs which enclose the corresponding tooth of the rotor on four sides, at least one of said elastic tabs being supported under the tab of the flange and at least two of said elastic tabs bearing against the bearing surface of the flywheel; the tab of the rim has a free end forming an enlarged head, the elastic tab which is supported under said tab of the rim having two flaps arranged on either side of the tab of the flange in support behind the enlarged head of said tab, to secure the cage and the corresponding tooth of the rotor with the flywheel; - the cage is made of austenitic stainless steel; the flywheel has a central bulge and a peripheral bulge separated from each other by an annular thinning, the teeth of the rotor being fixed on one of the bulges and the stator being placed opposite the thinning; the control and power unit is adapted to generate an excitation current as a function of a speed of rotation of the rotor, to maintain the induced voltage substantially constant; - the receiving coils are suitable for producing a three-phase current at variable frequency and for sending this three-phase current to the control and power unit, said control and power unit comprising a cycloconverter for transforming said three-phase current into an alternating current of fixed frequency; the receiving coils are adapted to generate a three-phase current and to send this three-phase current to the control and power unit, said control and power unit being adapted to rectify said three-phase current into a direct current and then to transform said current continuous in alternating current of fixed frequency by an inverter; the stator teeth are angularly distributed about the axis of rotation and carry alternately an excitation coil and a receiving coil, the rotor teeth being angularly distributed around the axis of rotation, the rotor and stator teeth being arranged so that at any time, at least one of the teeth of the rotor covers at least one pair of two adjacent teeth of the stator by defining a magnetic circuit between these two teeth of the stator, said tooth of the rotor respectively covering said two teeth of the pair of adjacent teeth respectively on first and second surfaces, the smallest of which defines a magnetic flux passage section, and the teeth of the rotor and of the stator being shaped so that the sum of the magnetic flux passage sections of all the pairs of adjacent stator teeth magnetically connected by the rotor teeth is substantially constant over time.

Other characteristics and advantages of the invention will appear during the detailed description of several of its embodiments, given by way of nonlimiting examples, with regard to the attached drawings.

In the drawings: FIG. 1 represents a schematic view of an electricity production system according to an embodiment of the invention, comprising a rotary electric machine whose rotor is fixed to a flywheel, FIG. 2 represents a radial sectional view of the rotary electric machine equipping the system of FIG. 1, FIG. 3 is a sectional view along line III-III of FIG. 2, FIG. 4 represents an enlarged part of FIG. 1, showing in detail the cooling arrangements of the rotary electric machine, FIG. 5 is a view similar to FIG. 2, in a variant of the invention, and FIGS. 6 and 7 are detailed views showing the fixing of the teeth of the rotor on the flywheel, in another embodiment of the invention.

FIG. 1 represents a schematic view of an electricity production system comprising a storage flywheel and a rotary electric machine. This system is described in detail in document WO 01/63729 and only its main elements are described here.

The electricity production system 1 comprises: a heat engine 2, a mechanical speed variator 3 driven by the motor 2, a clutch 4 driven by the speed variator 3, a flywheel 5 rotating around an axis of rotation Z (in this case vertical) and driven by the motor 2 via the variator 3 and the clutch 4, the flywheel 5 being made for example of austenitic stainless steel, a rotary electric machine, and in particular a generator 6 making it possible to transform the kinetic energy of the flywheel 5 into electrical energy, and an electronic control and power unit 7.

The flywheel 5 preferably rotates in a vacuum enclosure 8 which also contains the generator 6 and the clutch 4.

The enclosure 8 and the heat engine 2 are preferably mounted on anti-vibration supports 9, some of which rest on a concrete base 9a or the like. The control and power unit 7 controls the mechanical speed controller 3, using an electric motor 10, and said control and power unit also controls the clutch 4 and the generator 6. The unit control and power 7 receives the electric power from the generator 6 and transforms it into an electric voltage in accordance with the expectations of the user.

The steering wheel 5 advantageously has a shape with two symmetrical bulges of revolution around the axis Z, one at the center 11, the other at the periphery 12, with an annular thinning 13 between the two bulges 11, 12. The rotor 14 of the generator 6 is fixed to one of the two bulges 11, 12 (in particular the outer bulge 12). The stator 15, integral with the enclosure 8, is in turn placed at the level of the thinning 13.

The advantage of this embodiment is that the generator 6 is thus perfectly integrated in the flywheel 5: the rotor 14 is at a place where its attachment is easy and where it is well supported by the structure of the flywheel 5; the stator 15 is inserted in an available location, so that the size of the flywheel / generator 5, 6 is identical to that of the flywheel 5 alone. These provisions are especially advantageous compared to previously known solutions, which had many drawbacks: if the generator 6 is separate from the flywheel 5, the axial size becomes very large, and it is necessary to add bearings and a coupling;

- If the generator 6 is integrated on the periphery of the flywheel 5, the radial size becomes very large and the rotor 14 is subjected to a large centrifugal force; - Finally, if the generator 6 is integrated in the center of the flywheel 5, it must be pierced, which locally increases the level of stress and therefore requires a heavier flywheel 5.

Figure 2 shows the generator 6 of Figure 1 for a preferred embodiment. The magnetic circuit, consisting of the rotor 14 and the stator 15, is made of ferromagnetic material suitable for high frequencies, that is to say divided and not massive: it can be thin sheets cut and stacked, or sintered powder. The rotor 14 advantageously consists of four teeth 16 each having the shape of an angular sector extending over approximately 60 ° around the axis Z. These teeth 16 are preferably independent of each other so that during rotation at high speed they are not subjected to too much stress, which could occur if they were united in a monobloc crown.

The stator 15 advantageously consists of a crown comprising twelve teeth 17, each extending over a little less than 30 ° around the axis Z. The base of the teeth 17 is thinned in order to provide space for winding a coil 18a, 18b, 18c, 18d around each of them. One coil out of two (referenced 18a in FIG. 2) is traversed by an excitation current imposed by the control and power unit 7. These excitation coils 18a are connected alternately, i.e. by producing a magnetic field alternately outwards and inwards of tooth 17, as indicated by the arrows in FIG. 2 (in other words, the magnetic fields P two coils 18a of the same pair of diametrically opposite coils are aligned and in the same direction).

The other coils 18b, 18c, 18d are subjected to an alternating induced voltage caused by the passage of the teeth 16 in front of the teeth 17 during the rotation of the rotor 14. These receiving coils 18b, 18c, 18d are connected in pairs (the diametrically opposite coils being connected together), so that the coils 18b, 18c, 18d respectively form three phases U, V, W, as shown in Figure 2.

The excitation current is most generally of the continuous type, and it is regulated so that the induced output voltage is constant. Indeed, for a given current, the voltage induced by the rotation of the rotor 14 varies with the speed of rotation. If the demand is very low, it is even possible to stop the excitation current, which leads to totally zero losses in the generator 6. Finally, a three-phase generator 6 is perfectly suited for mounting on a storage flywheel 5 energy. In fact, the only losses to the rotor 14 are due to the variable magnetic field in the teeth 16. As care has been taken to produce these teeth 16 in a material with low losses, and that the excitation field is regulated as a function needs, we have the lowest possible losses.

In the case of a three-phase generator 6 with regulated voltage like that of FIG. 2, the control and power unit 7 can advantageously include a cycloconverter 7a for generating an alternating voltage of fixed frequency. This technology offers the advantage of better performance than the conventional technology of rectifying and then undulating the voltage produced, by means of an inverter 7a instead of the cycloconverter. The solution of the inverter can however be envisaged in the context of the present invention.

Another possibility is to vary the excitation current periodically, at the frequency of the voltage desired by the user, so as to directly produce an output voltage varying at the right frequency, which it suffices to rectify to eliminate the high frequency due to rotation.

One can note an important characteristic of the generator 6 of FIG. 2: the total reluctance of the magnetic circuit surrounding all of the coils 18a which are excited by the current remains substantially constant during the rotation of the rotor 14.

Indeed, the teeth 16 of the rotor form, between certain teeth 17 adjacent to the stator, magnetic circuits whose field lines B are shown for one of the teeth 16 in FIG. 2. These magnetic circuits each have a certain passage section magnetic flux, which can be defined as being the smaller of the two outer surfaces of two adjacent teeth 17, located opposite the tooth, 16 concerned. For example, there is shown in bold lines in FIG. 2, for one of the teeth 16 of the stator, the three facing surfaces of the tooth 16 SI, S2, S3 belonging respectively to three adjacent teeth 17 covered at least partially by said tooth 16. These three adjacent teeth 17 form two pairs of adjacent teeth: a first pair of adjacent teeth having surfaces S1, S2 respectively opposite tooth 16 and forming a first magnetic circuit with said tooth 16, and a second pair of adjacent teeth 17 respectively having surfaces S2, S3 opposite the corresponding tooth 16 and forming a second magnetic circuit with said tooth 16. In the example shown in FIG. 2, the surfaces S1 and S3 are lower at the surface S2, so that the magnetic flux passage section of the first pair of teeth 17 is SI and the magnetic flux passage section of the second pair of teeth 17 is S3.

It can be seen that when the rotor turns clockwise in the example of FIG. 2, the surface S3 gradually increases and the surface Si decreases by as much, until the tooth 16 considered begins to cover a new tooth 17. In all cases, each tooth 16 corresponds to a total cross section of substantially constant magnetic flux, equal to S1 + S3, that is to say equal to the external surface S2 of a tooth 17 complete. More generally, according to the invention, the constant total magnetic reluctance of the magnetic circuit formed by the set of teeth 16, 17 means that the sum of the magnetic flux passage sections corresponding to the different pairs of teeth 17 covered at least partially by the teeth 16 of the rotor, remains substantially constant over time.

Another advantageous arrangement of the generator 6 is that it is very easy to thermally insulate the rotor 14 from the flywheel 5, as shown in FIG. 3. It suffices to interpose a small thickness of thermal insulating material 20, such as for example l stainless steel or plastic. As the rotor 14 is the only rotating part where heat is produced, its temperature will become significantly higher than that of the flywheel 5, the presence of the insulator 20 offers the advantage of preventing the steering wheel from becoming too hot, which would reduce its mechanical resistance. It is much less annoying that the rotor 14 becomes hot; on the contrary, a high temperature increases its resistivity, which reduces losses, and increases radiation, which is the only mode of cooling in a vacuum. Radiation cooling can be further increased by placing on the rotor 14 one or more thermally conductive support plate (s) 21, in close thermal contact with the rotor 14, which increases the heat capacity and the surface area d 'program. Facing the support plate 21, one can place on the enclosure 8 of the steering wheel 5 one or more radiator (s) 22 collecting the radiation and discharging it into the air by fins 22a. If there is only one radiator 22, it can advantageously be annular and centered on the axis Z. As shown in FIG. 3, the stator 15 can be cooled using a water circuit 19, if the power to be dissipated is significant. If the power is low, the thermal conduction of the stator to the enclosure 8 of the flywheel 5 may be sufficient.

Another interesting arrangement consists in producing a control and power unit 7 which is reversible, that is to say capable of transmitting energy to the flywheel 5 through the generator 6, which then behaves like a motor. . The generator 6 of FIG. 2 can fully operate as a motor, provided that it is controlled correctly. Thus, if the system is connected to other sources of electricity, the flywheel 5 can be used to store the energy they produce. This is particularly interesting with renewable energy sources like the sun and the wind, whose production moments do not correspond to the consumption moments. Furthermore, as shown in FIG. 5, the generator 6 could be single phase instead of three phase. In this case, as shown in FIG. 5, the rotor 14 could comprise only three teeth 16 produced as described above and distributed regularly around the stator 15, which stator 15 could comprise only four teeth 17 each having the shape of an angular sector extending a little less than 90 ° around the Z axis.

The base of each tooth 17 is thinned, as in the example previously described, in order to manage the space for winding a coil, respectively 18a, 18b around each of them. Two coils 18a wound around the diametrically opposite teeth, called excitation coils, are traversed by an excitation current imposed by the control and power unit 7. These two excitation coils 18a are connected alternately, as described above, so as to produce in the corresponding teeth 17 aligned magnetic fields P and in the same direction (one of these magnetic fields P is therefore oriented radially inwards while the other is oriented radially outwards stator).

The other two coils 18b are subjected to an induced alternating voltage caused by the passage of the teeth 16 in front of the teeth 17 during the rotation of the rotor 14. These receiving coils 18b are connected together so as to form a phase U as indicated on the Figure 5. As already explained with reference to Figures 1 to 4 the excitation current is advantageously continuous and regulated by the power control unit 7 so that the output voltage generated by the coils 18a is constant.

As in the first embodiment of the invention, the total magnetic reluctance of the current magnetic circuit surrounding all of the coils 18a which are excited by the current remains substantially constant during the rotation of the rotor 14. In other words, the sum of the magnetic flux passage sections between the pairs of teeth 17, the two teeth of which are magnetically connected by the teeth 16 of the rotor, remains constant over time during the rotation of the rotor. Finally, FIGS. 6 and 7 represent a particularly advantageous method of fixing the teeth 16 on the flywheel 16.

According to this embodiment, each tooth 16, which is made of a magnetic material of relatively low mechanical strength, is disposed inside an annular flange 23 of the flywheel 5, between an axial shoulder 24 of said flywheel 5 and a tab 25 which extends radially inwards from the free end of the annular rim 23. In order to limit the losses by eddy current, the tooth 16 is fixed without drilling or welding, simply by means of a cage 26 made of sheet steel, which surrounds the tooth 16 on five sides. The cage 26 leaves the inner face of the tooth 16 free towards the stator for the transmission of the magnetic field. In addition, said cage 26 is force fitted between the bearing face 24 and the tab 25, and prevents any direct contact between the tooth 16 and the flywheel 5.

The cage 26 has a rear face 27 which has a cylindrical shape of revolution centered on the axis Z, so as to perfectly match the inner face 23a of the rim 23 as well as the outer shape of the tooth 16, to transmit optimally to the flywheel 5 the centrifugal forces undergone by the tooth 16 during the rotation of the flywheel. On its four other faces, the cage 26 has elastic tabs 28 which can be advantageously folded so as to form corrugations and which are applied elastically against the four lateral faces of the tooth 16 so as to maintain it by elasticity. This maintenance is all the more effective as the two lateral faces 16a of the tooth 16 converge towards the axis Z, so that the elastic tabs 28 applied against these lateral faces 16a prevent any movement of the tooth 16 towards the axis Z (see FIG. 7). The lower legs 28 may for example be two in number, and they are supported on the shoulder 24 of the flywheel. The cage 26 can moreover comprise a single upper tab 28 which advantageously cooperates with the tab 25 of the flywheel to immobilize the cage 26 and the tooth 16 relative to said flywheel.

To this end, in the example shown, the central upper tab 28 of the cage 26 is not only bearing under the tab 25, but also it has two flaps 29 which are folded on either side of the tab 25 of the flywheel, as can be seen in FIG. 7. Preferably, the tab 25 of the flywheel can have a substantially T-shape, with an enlarged head at its radially inner end: in this case, the two flaps 29 of the central upper tab 28 engage behind the enlarged head 25a of the tab 25 and completely secure the cage 26 and the tooth 16 relative to the flywheel 5.

The cage 26 can advantageously be made of austenitic stainless steel, which has a relatively low thermal conductivity compared to other steels, which limits the heat transmitted by conduction of the tooth 16 towards the flywheel 5. Finally, this steel is non-magnetic, which considerably reduces the magnetic field leaks from tooth 16 towards the flywheel 5, and therefore consequently the energy losses by eddy current in said flywheel 5.

Note also that the tab 25 of the flywheel covers only a small part of the surface of the tooth 16 and of the cage 26 in the axial direction, so that said tab 25 does not substantially interfere with the dissipation of thermal energy from tooth 16 to enclosure 8 of the flywheel.

Claims

1. Device comprising a rotary electric machine which comprises a rotor (14) rotating around an axis of rotation (Z) and a stator (15), the rotor (14) comprising a plurality of teeth (16) made of divided ferromagnetic material but having neither conductor nor permanent magnet, the stator (15) comprising a plurality of teeth (17) of divided ferromagnetic material, oriented towards the rotor, each tooth (17) of the stator (15) being surrounded by a coil (18a -18d), the coils (18a-18d) comprising on the one hand excitation coils (18a) which are electrically connected to a control and power unit (7) to receive an excitation current, and on the other hand, receiving coils (18b-18d; 18b) adapted to produce an induced voltage when the rotor (14) rotates, characterized in that the teeth (16, 17) of the rotor and the stator are arranged so that the reluctance total of a magnetic circuit formed by the set of teeth (16, 17) of the rotor e t of the stator remains substantially constant when the rotor turns.

2. Device according to claim 1, in which the teeth (16) of the rotor (14) are four in number and each cover an angular sector of approximately sixty degrees centered on the axis of rotation (Z), the teeth ( 16) being angularly distributed around the axis of rotation (Z), the teeth (17) of the stator (15) are twelve in number and each cover an angular sector of about thirty degrees centered on the axis of rotation ( Z), the excitation coils (18a) are six in number and are coupled in pairs of diametrically opposite excitation coils, and the receiving coils (18b-18d) are six in number and are coupled in pairs of diametrically opposite receiving coils.

3. Device according to claim 1, wherein the teeth (16) of the rotor (14) are three in number and each cover an angular sector of about sixty degrees centered on the axis of rotation (Z), the teeth ( 16) being angularly distributed around the axis of rotation (Z), the teeth (17) of the stator (15) are four in number and each cover an angular sector of approximately ninety degrees centered on the axis of rotation (Z), the teeth (16) of the rotor being angularly distributed around the axis of rotation (Z), the excitation coils (18a) are two in number and are coupled in a pair of coils diametrically opposite excitation, and the receiving coils (18b) are two in number and are coupled into a pair of diametrically opposite receiving coils.

4. Device according to any one of the preceding claims, in which the teeth (16) of the rotor (14) are fixed to a flywheel (5).

5. Device according to claim 4, in which the flywheel (5), the rotor (14) and the stator

(15) are contained in a vacuum enclosure (8).

6. Device according to claim 5, wherein the teeth (16) of the rotor are arranged opposite a radiator (22) integral with the vacuum enclosure (8), said teeth (16) of the rotor being adapted to dissipate thermal energy by radiation to said radiator (22).

7. Device according to any one of claims 4 to 6, wherein the teeth (16) of the rotor (14) are independent of each other.

8. Device according to one of claims 4 to 7 wherein the teeth (16) of the rotor (14) are thermally isolated from the flywheel (5).

9. Device according to any one of claims 4 to 8, in which the flywheel is made of austenitic stainless steel.

10. Device according to any one of claims 4 to 9, in which the flywheel comprises at least one flange (23) which has a radially inner face (23a) against which the teeth (16) of the rotor bear. (14).

11. Device according to claim 10, in which the flange (23) has a free end extended radially inwards by a tab (25) at each tooth (16) of the rotor, said tab (25) of the flange covering partially the corresponding tooth (16) of the rotor.

12. Device according to claim 11, in which the tooth (16) of the rotor is enclosed by a cage (26) itself fitted by force between the tab (25) of the flange

(23) and a bearing surface (24) belonging to the flywheel, said cage (26) being in abutment against the radially inner face (23a) of the flange (23), and said cage

(26) isolating the corresponding tooth (16) from any direct contact with the flywheel (5).

13. Device according to claim 12, in which the cage (26) comprises: a rear face (27) interposed between the corresponding tooth (16) of the rotor and the radially inner face (23a) of the flange (23), and several tabs elastic bands (28) which enclose the corresponding tooth (16) of the rotor on four sides, at least one of said elastic tabs (28) being supported under the tab (25) of the rim (23) and at least two of said elastic tabs (28 ) being in abutment against the bearing surface (24) of the flywheel.

14. Device according to claim 13, in which the tab (25) of the rim (23) has a free end (25a) forming an enlarged head, the elastic tab (28) which is supported under said tab (25) of the rim (23) having two flaps (29) arranged on either side of the tab (25) of the flange (23) bearing behind the enlarged head (25a) of said tab, to secure the cage

(26) and the corresponding tooth (16) of the rotor with the flywheel.

15. Device according to any one of claims 12 to 14, wherein the cage (26) is made of austenitic stainless steel.

16. Device according to any one of claims 4 to 15, in which the flywheel (5) has a central bulge (11) and a peripheral bulge (12) separated from each other by an annular thinning (13), the teeth (16) of the rotor being fixed to one of the bulges (11, 12) and the stator (15) being placed opposite the thinning (16).

17. Device according to any one of the preceding claims, in which the control and power unit (7) is adapted to generate an excitation current as a function of a speed of rotation of the rotor (14), to maintain substantially constant the induced voltage.

18. Device according to any one of the preceding claims, in which the receiving coils (18b-18d) are adapted to produce a three-phase current at variable frequency and to send this three-phase current to the control and power unit (7 ), said control and power unit comprising a cycloconverter (7a) for transforming said three-phase current into an alternating current of fixed frequency.

19. Device according to any one of claims 1 to 17, in which the receiving coils

(18b-18d) are adapted to generate a three-phase current and to send this three-phase current to the control and power unit (7), said control and power unit (7) being adapted to rectify said three-phase current by a direct current then to transform said direct current into an alternating current of fixed frequency by an inverter (7a).

20. Device according to any one of the preceding claims, in which the teeth (17) of the stator are angularly distributed equally around the axis of rotation (Z) and carry alternately an excitation coil (18a) and a reception coil. (18b-18d; 18b), the teeth (16) of the rotor being angularly distributed equally around the axis of rotation (Z), the teeth (16, 17) of the rotor and the stator being arranged so that at all times, at least one of the teeth (16) of the rotor covers at least a pair of two adjacent teeth (17) of the stator by defining a magnetic circuit (B) between these two teeth (17) of the stator, said tooth (16) of the rotor covering respectively said two teeth (17) of the pair of adjacent teeth respectively on first and second surfaces, the smallest of which (SI, S3) defines a magnetic flux passage section, and the teeth (16, 17) of the rotor and of the stator being shaped so that the sum of the flow passage sections x magnetic of all the pairs of adjacent teeth (17) of the stator magnetically connected by the teeth of the .rotor (16) is substantially constant over time.